As illustrated in U.S. Pat. No. 2,731,437, issued to Bender, et al. on Jan. 17, 1956, the reaction of one equivalent of a mercaptan terminated polysulfide with one equivalent of epichlorohydrin in the presence of one equivalent of alkali to form an epoxide capped polysulfide is known. This reference teaches that the reaction is exothermic, and should be carried out in the presence of a diluent such as an alcohol or an ether to avoid an excessive rise in temperature. Bender, et al. does not teach removal of water during the reaction. These two deficiencies of the Bender, et al. method make the process impractical because it requires several days to complete.
A reaction somewhat analogous to that of Bender, et al. has previously been used to form epoxide capped aromatic polyphenols. This reaction is illustrated in British Patent Specification 897,744, published May 30, 1962; U.S. Pat. No. 3,980,679, issued to Becker on Sep. 14, 1976; and Fujisawa, "Synthesis of Poly(4-hydroxy-3,5-di-t-butylphenyl glycidyl thioether)", Polymer Letters Edition, Vol. 12, pp. 557-559 (1974). This reaction is not entirely the same as the present one, however, for two reasons. First, of course, is the difference between phenols and polysulfides. Second, the phenolic reaction sometimes requires an additional prereaction step before the alkali is added, during which water must be present.
The previously cited British specification suggests removing water from the reaction mixture by azeotropic distillation while alkali is being added to the reaction. The azeotrope is separated into water and epichlorohydrin, and the epichlorohydrin is returned to the reaction mixture. This removal of the water by-product and return of epichlorohydrin reactant tends to drive the reaction to the right. On page 2, lines 54-7, this reference suggests the presence of various solvents in the reaction mixture, such as benzene, toluene, ether, dioxane, acetone, etc. (Reference herein to a "solvent" does not include epichlorohydrin, unless otherwise indicated.) Some of these solvents are water miscible, and others are water immiscible. The reference does not suggest any difficulty in separating the product from the reaction mixture in the event a polar solvent is used.
The Becker patent cited above suggests that the epoxide capping reaction of a phenol requires about 40 hours unless certain tin catalysts are added to the first stage of reaction, before the alkali is added. (See col. 1, line 65 to col. 2, line 56). Example 1 employs xylene and example 4 employs isobutanol as reaction solvents, and no suggestion is made in the reference that the presence of a solvent lengthens the reaction or separation times.
In the Fujisawa reference, the reaction of epichlorohydrin, a phenol, and sodium hydroxide is disclosed to require about 40 hours, in the absence of any solvent for the epichlorohydrin.
The art cited above relating to end-capping phenolic reactants with epoxide groups does not suggest that it is advantageous to avoid polar reaction solvents to shorten the reaction or separation times.